The inquiry into the collapse of the Canterbury Television building has heard it was built using "permissible loopholes" in the building code of the day.
The Canterbury Earthquakes Royal Commission is investigating why the CTV building collapsed in the 6.3-magnitude earthquake on 22 February 2011, killing 115 people.
Professor John Mander has been called for a third time to give evidence. He has previously said that because the building survived the 7.1-magnitude earthquake centred in Darfield in September 2010, it was a good design.
On Thursday, he told the commission the use of ductile walls and non-ductile frames was not good practice but was permissible.
He said that by the time the Boxing Day quake in 2010 hit, the building's response capabilities were "eating into its reserve capacities".
Dr Mander told the inquiry it was the Boxing Day earthquake that probably caused the damage that made the building collapse in February 2011.
He said that because the quake was centred under Cashel Street, it would have caused irreparable damage.
Dr Mander said this should have rung alarm bells but those alarm bells fell on deaf ears.